1. Technical Field
This invention relates generally to the field of semiconductor manufacturing and, more specifically, to photo resist compositions including both photo acid and photo base components that are adapted to produce a hybrid resist image.
2. Background Art
The need to remain cost and performance competitive in the production of semiconductor devices has caused continually increasing device density in integrated circuits. To facilitate the increase in device density, new technologies are constantly needed to allow the feature size of these semiconductor devices to be reduced. For the past 20 years, optical lithography has driven the device density and the industry has resorted to optical enhancements to allow increasing densities. As an example, some such enhancements include over exposing/over developing, hard and soft phase shifts, phase edge masks, and edge shadowing. Unfortunately, such enhancements tend to offer only minor increases in density and the limits of optical enhancements appears inevitable in the near future. Further, in the scaling of lithography, the physical limits of some of the parameters previously relied upon to print smaller features are being approached. For optical lithography, wavelength and numerical aperture (NA) are reaching their limits at this time. New printing methods are needed to allow scaling of devices by other means than traditionally used. As described in the related applications incorporated by reference above, hybrid resists provide one means of accomplishing this goal, however, existing hybrid photo resist compositions also have limitations.
Conventional positive and negative tone photo resist used in optical lithography are characterized by a dissolution curve in which there is a single transition from a first dissolution rate to a second dissolution rate as the resist is exposed to increasing levels of actinic radiation. In a positive resist, the initially unexposed resist is practically insoluble in developer, while the exposed resist becomes more soluble as the exposure dose is increased above a threshold value. For a negative resist, similar behavior is observed, except that the initially unexposed resist is soluble in developer, and the exposed area is rendered practically insoluble. Because of this differential solubility between the exposed and unexposed resist areas, it is possible to form a pattern, or resist image, in the resist film. Essentially, the soluble areas of the resist dissolve in developer to become spaces in the resist, while the insoluble areas remain as lines of resist material. The resist image thus formed can be used to fabricate integrated circuit devices.
In an ideal situation, an exposure tool would only allow actinic energy to expose the resist material through a reticle of a mask, thus providing sharp edges for lines and spaces in a resist image. However, diffraction patterns are formed at to the edges of the reticle, resulting in partial exposure of the resist about the edges of the a reticle. The partial exposure yields a resist profile that exhibits some slope at the transition from a line to a space rather than a sharp, vertical profile at the edge of a line, as would be present in an ideal resist image. A hybrid resist takes advantage of the slope in the exposure profile to produce a frequency doubled resist image. That is, where a positive resist will produce a space as a resist image, a hybrid resist will produce a space/line/space as a resist image in the same area. Thus, the number of features produced in the resist image are doubled in frequency.
Current formulations of hybrid resist use a balancing of cross-linking and solubility inhibition to express both positive and negative tone chemistry in the image formation process. This type of formulation allows a sub-lithographic space to be printed at the edges of the aerial image produced when radiation passes through the reticle of a mask. The more highly exposed center of the aerial image yields a line in the resist image, thus, the space/line/space effect is obtained. Current formulations, however, are not capable of printing a sub-lithographic line at the edges of the aerial image. It is desirable to print a sub-lithographic line as some applications for a hybrid resist in the production of semiconductors require a line pattern instead of a space pattern. Hybrid resist formulations that do not rely on the cross-linking mechanism are also desirable since the cross-linking mechanism is not currently available for some types of actinic radiation, such as 193 nanometer (nm) radiation.
Also, current formulations of hybrid resist possesses the advantage that the width of the sub-lithographic space is generally unchanging as the exposure dose and the reticle dimension are changed. This allows very precise image control for the space width within each chip, across each wafer, and from one batch of product wafers to the next. Nevertheless, the result of this advantage is that it can be difficult to alter the width of a sub-lithographic space in a hybrid resist image. In a conventional resist, altering the reticle dimension or exposure dose are the techniques commonly used to alter the resist image dimensions.
In keeping with the above discussion, it is apparent that current hybrid resist formulations possess the advantage of printing smaller features than presently possible through the scaling of lithography, due to the limits of wavelength and NA. For example, a 0.5 micrometer reticle opening could produce two 0.2 micrometer spaces and a 0.2 micrometer line. Despite this accomplishment, it is still desirable to reduce the size of features that may be produced using hybrid resist to further the continual increase of device density in semiconductor manufacturing.
Accordingly, it would be an improvement in the art to provide a photo resist composition that produces a hybrid resist image, yet will print a line and does not rely on a cross-linking mechanism. Also, it would be an improvement for such a composition to enable altering the width of features in a hybrid resist image. Further, it would be an improvement to produce smaller features than possible with current hybrid resist formulations.
According to the present invention, a photo resist composition is provided including a polymer resin, a first photo catalyst generator requiring a first dose of actinic energy to generate a first catalyst capable of inducing a solubility change in the polymer resin, and a photo quenching agent generator requiring a second dose of actinic energy greater than the first dose to generate a quenching agent. When the such a photo resist receives a single exposure of actinic energy, the first photo catalyst induces a solubility change in areas of the photo resist exposed to the first dose, while the photo generated quenching agent prevents a solubility change in areas of the photo resist exposed to the second dose. As a result, the photo resist exhibits a dissolution curve having a plurality of phases. That is, at least two solubility changes may be induced in the photo resist. A first solubility transition occurs at a low dose and a second solubility transition occurs at a higher dose. A photo resist exhibiting such a dissolution curve will produce a hybrid resist image upon development that includes at least one line and at least one space within an exposed region of the photo resist as the result of a single exposure to actinic energy. Depending on the formulation, either a space or a line may be printed at the edge of an aerial image produced by an exposure where diffraction effects reduce exposure dose at the image edge.
If a second photo catalyst generator is included requiring a third dose of actinic energy, greater than the second dose, to generate a second catalyst capable of inducing a solubility change, then it may overcome the quenching agent and produce a third solubility change, yielding a tri-phase dissolution curve. That is, a third solubility transition may occur after the second solubility transition at a dose beyond the higher dose. A photo resist exhibiting such a dissolution curve will produce a hybrid resist image upon development that includes either a space/line/space/line/space combination or a line/space/line/space/line combination within a single exposed region. Thus, an increased number of features, as well as potentially smaller features, may be produced compared to conventional hybrid resist formulations.
Further, a quenching agent additive may be included in the photo resist composition that shifts the first solubility transition of the dissolution curve caused by the first catalyst toward a second solubility transition of the dissolution curve caused by the photo generated quenching agent. A photo resist exhibiting such a change in the dissolution curve will produce a space or a line in the resist that is reduced in width compared to a corresponding space or line created without the quenching agent additive. Thus, altering the width of features, potentially sub-lithographic features, in a hybrid resist is enabled.
By way of example, the first and second catalyst may be an acid or a base and the quenching agent may respectively be a base or an acid.
The foregoing and other features and advantages of the present invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.